1. Field of the Invention
The present invention relates to a trapping device used in, for example, an evacuation system for evacuating a vacuum chamber in a semiconductor manufacturing apparatus.
2. Description of the Related Art
A conventional evacuation system will be described with reference to FIG. 9. A vacuum chamber 101 is a processing chamber for processing semiconductor devices through processes such as etching or chemical vapor deposition (CVD). The processing chamber 101 is communicated with a vacuum pump 103 through a pipe 102. The vacuum pump 103 is used to raise the gas pressure of the spent gas from the processing chamber 101 to an atmospheric pressure, and in the past, oil-lubricated rotary pumps were common but modern pumps are mainly so-called dry pumps.
When the degree of vacuum required in the processing chamber 101 is higher than the performance capability of the dry pump 103, an ultra-high vacuum pump such as a turbo-molecular pump is provided upstream of the dry pump. A gas scrubber 104 is provided in a downstream location of the vacuum pump 103, and depending on the characteristics of the exhaust gases, those gases which cannot be exhausted to the atmosphere directly, such as those that are poisonous or explosive, are treated in this device by such processes as adsorption, decomposition and absorption, and only the harmless gases are exhausted into the atmosphere. The pipe 102 is provided with valves in desired locations.
In such conventional vacuum systems, if the reaction byproduct contains a substance having a high sublimation temperature, that substance will leave a solid residue in the process of pressure rise and, in some cases, precipitate in the vacuum pump to cause failure of the pump.
For example, when aluminum is subjected to an etching process, using typical process gases such as BCl.sub.3, Cl.sub.2, the exhaust gas from the processing chamber 101 will contain a reaction byproduct AlCl.sub.3 as well as residual gaseous BCl.sub.3 and Cl.sub.2.
Among these gases, AlCl.sub.3 does not precipitate on the intake side of the vacuum pump where it has a low partial pressure, but while it is being pressurized to raise the partial pressure, it precipitates inside the vacuum pump and the solid particles adhere to the interior wall of the vacuum pump. This phenomenon is a cause of pump failure. Similar problems are encountered when byproducts such as (NH.sub.4).sub.2 SiF.sub.6 and NH.sub.4 Cl are formed for producing SiN thin film by CVD.
Conventional remedial approaches include:
(1) The vacuum pump is heated to maintain the pump at a high temperature so that the exhaust gas would not precipitate solid particles inside the pump and is eliminated through the pump in a gaseous state.
(2) A water-cooled trap is provided in an upstream location (intake side) of the vacuum pump so as to precipitate potential particles before they enter the vacuum pump.
In the first approach, although it is effective in preventing precipitation inside the vacuum pump, precipitation can still occur in a gas scrubber disposed downstream of the vacuum pump, and the resulting blockages of the filtering layers presented a serious operational and maintenance problems. In the second approach, the system has to be shutdown for cleaning of the traps resulting that the system productivity is sacrificed.
Therefore, it is desirable first to be able to trap potential particles in the spent exhaust gas and to regenerate the intercooler automatically without having to shut down the system. Such a system would assure long service life of the pump, provide protection for gas scrubbers and reduce time loss so that the operational reliability of the manufacturing system will be improved. It is further desirable that the system is able to reduce the cost of building and operating the trapping device.